Alternately crimped staple fiber



y 1962 B. M. BOHMFALK 3,034,196

ALTERNATELY CRIMPED STAPLE FIBER Filed March 18, 1960 FIG. I 4FIG.2

INVENTOR BARBARA M. BOHMFALK ATTORNEY 3,3 4,195 Patented May 15, 1952Fic- This invention relates to textile fibers and more particularly tonovel, synthetic, staple-length fibers.

It has been a long-sought goal of the synthetic fibers industry toproduce, from synthetic fibers, wearing apparel fabrics which wouldresemble fabrics made of prestige animal fibers such as wool andcashmere. Such fabrics would be characterized in having the desirablebulk, cover, resiliency, and hand of the animal fibers and,additionally, would possess the desirable properties of synthetic fiberssuch as decreased shrinkage, resistance to insecticidal damage, ease ofcare, and increased durability. The approach generally taken towardaccomplishing this goal has been to convert synthetic fibers, which arenormally produced as straight fibers of indefinitely long length, intoshort-length staple fibers having a length roughly comparable to thelength of the animal fibers, and processing these staple fibers intoyarn and fabric, using methods and equipment similar to those used onthe animal fibers. The synthetic staple fibers, in the course of theirproduction, are often provided with fairly uniform deformations orcrimps throughout the length of the staple fiber so that the staplefibers will be non-straight and thus more closely resemble the animalfibers. The crimp may be temporary or durable. Temporary crimp is usefulmerely in improving web cohesion during carding operations, thuspermitting the synthetic staple to be processed into spun yarns onequipment designed for W001; but this crimp is not retained in the finalfabric in its normal use. Durable crimp, in addition to aiding yarnspinning, is retained by the staple fibers in the spun yarn or fabricproducts, providing bulkier spun yarns, and fabrics having the bulk,cover, and resiliency of wool fabrics. However, it is generally foundthat the synthetic fabrics lack the hand of wool or cashmere fabrics,and in addition present a pilling problem during the course of fabricuse which is not encountered in fabrics of animal fibers. Various fiberor fabric treating methods have been employed in efforts to reducepilling and to improve fabric hand, but very few of the treatments areefiective without deleterious effects, nor do they provide desirableeifects which are durable for the life of the fabric.

It is therefore an object of the present invention to provide syntheticstaple fibers which can be formed into pill-resistant fabric-s having acashmere-like hand. It is another object of the present invention toprovide synthetic staple fibers which can be formed into pill-resistantfabrics resembling cashmere fabrics. It is another object of thisinvention to provide pill-resistant fabrics made from durably crimped,synthetic staple fibers, which fabrics feel like wool or cashmere andresist shrinking and insecticidal damage. Other objects and advantageswill be apparent from the following specification and appended claims.

The objects of the present invention are accomplished by providing asynthetic, intermittently crimped, staplelengtn filament of l to '15denier having a durably crimped portion and at least one essentiallystraight terminal portion, said crimped portion comprising between and75% of the unextended or crimped filament length, said crimped portionshaving a crimp index between 8% and The intermittently crimped filamentsmay be prepared by intermittent exposure of a continuous strand offibers which are spontaneously crimpable by thermal or chemical means,to the necessary crimp-inducing thermal or chemical means, and cuttingthe strand into staple lengths at points on the uncrimped por ions ofthe strand. Alternatively, the intermittently crirnped filaments may beprepared from crimp-settable fibers by intermittent application ofmechanical crimp, simultaneously with, or followed by, a setting orstabilizing operation.

Throughout the specification and claims, by staple fibers it is meantfibers having an extended, i.e., uncrimped, length'from about 0.5 inchto about 5 inches. By extended lengt it is meant the shortest length towhich the staple fiber must be elongated by tension to remove all thecrimps and produce a temporarily completely straight fiber. Upon releaseof the tension, the fiber will spring back to its original, crimpedconfiguration.

The crimp index is defined by the formula:

7 crimp index extended length minus crimped length) (extended length)'and is customarily used to predict the performance of a staple fiberduring carding and drafting on cotton, woolen, and worsted systems.Thevalue of the crimp index is dependent upon the frequency andamplitude of the crimp and its general geometric configuration. For thepurposes of the present invention the crimp frequency is preferably inthe range of 5 to 30 crimps per inch. The crimp amplitude is the averageamplitude of the peakto-peak vertical deflection of a planar projectionof the crimped portion of the staple fiber, and is preferably in therange of 0.05 mm. to 0.5 mm.

In accordance with the present invention, the durably crimped portionmust have a crimp index between about 8% and 35%. When a major portionof the fiber length is crimped, i.e., from about 50% to the crimp indexmay be near the lower limit. Conversely, when a minor portion iscrimped, i.e., from about 25% to 50%, the higher crimp index values arepreferred. If the crimp index falls below about 8%, web cohesion,necessary in carding operations, is lost. If the crimp index goes aboveabout 35%, the fabrics exhibit a tendency toward excessive pilling.

The nature of the invention and its objects and advantages will becomemore readily apparent from the following description and the drawingsrelated thereto in which:

FIGURE 1 illustrates the embodiment of a crimped staple fiber of thepresent invention in which both terminal portions are straight;

FIGURE 2 illustrates another embodiment of a crimped staple fiber of thepresent invention in which one of the terminal portions is straight;

FIGURE 3 is a diagrammatic illustration of suitable apparatus forpreparing the staple fiber shown in FIG- URE l; and

FIGURE 4 is a diagrammatic illustration of one form of apparatus forpreparing the staple fibers shown in FlGURES 1 and 2.

Referring now to FIGURE 4, a continuous filament tow of heat-crimpablematerial ll. is passed from a supply source, not shown, between a pairof counter-rotating rolls 12 and 13. Each of the sets of teeth 14 areadapted to be heated by internal electrical resistance heating elements15. A thermal insulating material 16 .prevents heating of the remainderof the surface of the rolls. Teeth 14 are arranged to intermesh at thepoint at which tow 11 passes between rolls 12 and 13, thereby impartingdurable crimp to a portion of tow. As the rolls rotate, knives 1'7engage the tow, forcing it against the edge of slots 18 in roll 13,thereby periodically severing it into staple fiber lengths. The staplefiber which has two straight terminal portions is collected in areceptacle, not

shown.

Alternatively, knives 17 and slots 18 are placed adjacent to thetrailing portion of teeth 14. With this arrange: ment, the tow issevered to provide a staple fiber having. one straight and one crimpedend.

In FIGURE 3, continuous tow 19 is supported on belt 20 by a plurality ofnonporous, fiat bars 21. The tow is held firmly against the resilientperipheral surface 22 of drum 23 bythe bars. A liquid or gaseouschemical crimping agent is directed by jets, not shown, in chamber 24ontothe exposed sections of tow, any excess agent being collected intray 25. The tow is periodically severed along the leading edge of bars21 by means of blade 26 of pneumatic knife 27. The severed staple isforwarded to a receptacle, not shown, by conveyor 28.

The invention will be further illustrated but is not intended to belimited by the following examples.

' EXAMPLE I A continuous 10,000denier tow of polyacrylonitrile fiberscontaining 3300 individual filaments, prepared by the dry, contiguousspinning of two different types of poly:

mer as described in the U.SQ application of Ryan and Tichenor, SerialNo. 793,502, filed February 16, 1959,,

steam, the tow is cut from the drum by a knife at each trailing edge ofthe bars. The crimped staple-length filaments thus obtained have onlyone straight end, have a vcrimpedportion extending about 45% of thecrimped length of the .staple fiber, have an average crimp amplitudev of0.27 mm., and a crimp index of. 14%. These fibers are processed into2/32s worsted count yarns by worsted system processing and are knit intoa fabric of 14 stitches/inch construction. The fabric thus obtained istested for pilling propensity using the apparatus and techniquesdescribed in Textile Research Journal, vol. 26, pages 731-735 (1956);Baird, Legere, and Stanley. In brief, the fabric swatches are tumbledinside a rubberlined cylinder in the presence of a small amount ofcotton lint. The fuzz and pills formed in this process are counted andcompared with standards representing known fabric pillingcharacteristics and having the following designations: (1)=no pilling,'(2)=slight but tolerable pilling, (3)=moderate pilling of borderlineacceptability, (4) .=unacceptable pilling, and ()=extremely highpilling. The fabric thus tested had a pill rating of 3 at twentyminutes. The fabric has a texture or hand very much I resemblingcashmere.

Asa control test, fibers of the same composition and same over-allstaple length are made which have a continuous over-all crimp. Yarn andfabric are made of these thoroughly crimped staple fibers by identicalprocesses as described above and similarly tested. The fabric has a verycoarse texture and has an unsatisfactory pill rating of 5.

EXAMPLE II The continuous tow of Example I is loosely wrapped around aone-foot diameter steel drum and clamped by flat steel bars one andone-half inches wide and spaced one-half inch from one'another andextending the length of the drum. The drum is rotated in a troughcontaining boiling water at a rate of one revolution per fifteenminutes. After drying at 130 C. for twenty minutes, the tow is cutthrough the middle of each clamped section through a one-sixty fourthinch slit provided in each bar and the bars are released. Thestaple-length filaments thus obtained have two straight ends and ahelically crimped portion in the center of each fiber comprising about25% of the crimped length of the filament.

The average crimp frequency is 14' crimps per inch andthe crimp index is35%. These fibers were processed into spun yarns of 5 woolen run countby woolen system processing and woven into a herringbone 2 x 2 twillusing ends and 40 picks per inch. The fabric thus obtained has ahandresembling cashmere and a pill rating of 3 units at twenty minutes.

As a control test, fibers of the same composition and same over-allstaple length are made having a continuous over-all crimp. Yarn andfabric are made of these thoroughly crimped staple'fibersfby identicalprocesses as described above and similarly tested. The fabric has acoarse texture and has an unsatisfactory pill rating of 5.

EXAMPLE III A continuous 900-denier :yarn of polyethylene terephthalatefilaments, produced according to. the process of US. Patent 2,604,689,having an individual denier of 3.1, is continuously wrapped onto therotating drum of the type shown in FIGURE 4,'haviug a one-foot diameter,and clamped by flat, steel bars inch wide, spaced 1% inches from oneanother, and extending the length of the drum. The unshielded yarn is.exposed to dry heat at a temperature of 150 C. provided by closelylocated electrical heating elements in reflectors, the drum beingrotated at a rate so as to permit five seconds of exposure at thistemperature. After contact with the dry heat source, the tow is cut fromthe drum by a knife acting at each trailing edge of the bars. Thecrimped staplelength filaments thus obtained have only one straight endand have a crirnped portion extending about 75% of the crimped length ofthe staple fiber. The crimped portion has an average crimp frequency of5 crimps per inch, and a crimp index of 8%. These fibers are processedinto 5 woolen run spun yarns by woolen system processing and made intothe fabric construction of Example II. The fabric thus obtained has asatisfactory pill rating of 2 and a texture or hand resembling cashmere.

, EXAMPLE IV A flattened, continuous tow of 3 denier per filament nylon(66) filaments is passed through the nip of the intermittently-toothedcounter-rotating wheels of FIGURE 4. The temperature of the teeth ismaintained at 420 F. and the rate of operation is such as to impart asetting action to the crimps produced. A double-straight-ended staplefiber, 2 /2 inches long is thus produced having a crirnped portionoccupying about 25% of the unextended length of the fiber and having acrimp index of 20% with a crimp frequency of about 30' crimps per inch.The staple fibers are converted into the fabric of Example I. The fabricthus obtained has a cashmere-like texture and a pill rating of 3. I

The products of this invention may be prepared from all types ofcontinuous filamentary materials which are capable of being given adurable crimp, for example thermoplastic linear synthetic polymers suchas polyamides, polyesters, polyacrylics, and polyvinyl compositions.Particularly suitable are the so-called spontaneously crimpable fibers,i.e., crimpable upon the application of heat or a suitable chemical,described in US. Patents 2,517,694 and 2,604,689, British Patent 808,213and Beligian Patent 562,290.

The fibers of this invention may be used in a variety of applications.They may be used alone or blended with other synthetic or natural fibersto provide spun yarns which may be used in various fabric constructionshaving a pleasing cashmere-like hand while exhibiting an acceptablelevel of pilling during the life of the garmet. The fibers can be ofsuch length that they are suitable for processing into textile yarns oncotton, woolen, or worsted machinery used in the manufacture of cottonor woolen spun yarns. V

The staple fibers of the present invention have a crimp mun-air which isdurable to textile manufacturing operations and to conventional textilecleaning procedures carried out during the life of a fabric or, which ifpulled out during textile processing, returns during textile finishing.Thus, the advantages of reduced pilling and cashmere-like hand areretained throughout the life of a textile fabric. Other uses for thenovel staple fibers of the present invention may be readily found inview of their unusual characteristics. Various chemical coatings may beemployed to enhance the cashmere-like efiects the compositions describedin copending application Serial No. 836,350 being typical.

As many widely diiferent embodiments of this invention may be madewithout departing from the spirit and scope thereof, it is to beunderstood that this invention is not to be limited to the specificembodiments thereof except as defined in the appended claims.

I claim:

1. A synthetic staple fiber having an essentially uniform cross sectionalong its length, a denier from about 1 to about 15, at least oneessentially straight terminal portion and a durably crimped portion,said crimped portion having a crimp index between about 8% and about35%, and a length comprising between about 25 and 75% of the unextendedlength of said fiber.

2. The staple fiber of claim 1 wherein both terminal portions arestraight.

3. The staple fiber of claim 1 wherein the crimped portion has a crimpfrequency between 5 and crimps per inch. e

4. The staple fiber of claim 1 wherein the crimped portion has a crimpamplitude between 0.05 and 0.5 mm.

5. 'A textile yarn comprised of synthetic staple fiber having anessentially uniform cross section along its length,

a denier from about 1 to 15, at least one essentially straight end and adurably crimped end, said crimped end comprising from about 25% to about75 of the unextended length of said fiber and having a crimp index be-vtween about 8% and about 6. A textile fabric having high resistance topilling and a cashmere-like hand comprising staple fiber having anessentially uniform cross section along its length, at least oneessentially straight terminal portion, a durably crimped portion and adenier from about 1 to 15, said crimped portion having a crimp indexbetween about 8% and about 35%, and a length comprising between about 25and of the unextended length of said fiber.

References Cited in the file of this patent UNITED STATES PATENTS

